In recent years, with the rapid development of digital cameras and camera cell-phones, a smaller-sized, high-resolution solid state image sensor is required. Since miniaturization of the solid state image sensor causes deterioration of sensitivity, light is collected efficiently to prevent the deterioration of device sensitivity by locating a collecting lens between an optical sensor part and a color filter, or above the color filter, or by forming an optical waveguide between an optical sensor part and a color filter. Examples of a common method of preparing the collecting lens or the optical waveguide include a method in which an inorganic film formed by a CVD process or the like is processed by dry etching and a method of applying a resin to a substrate and processing the substrate. In the former method, it is difficult to attain a refractive index of 1.65 to 1.90 which is optimum for a lens or an optical waveguide, and therefore the latter method is currently attracting attention.
Heretofore, for example, an alkali-soluble polymer such as polyamide acid, a compound having a phenolic hydroxyl group, a positive photosensitive resin composition containing a quinone diazide compound and inorganic particles (e.g., Patent Document 1), and a silicone copolymer having silsesquioxane having a phenol unit and a condensed polycyclic hydrocarbon radical (e.g., Patent Document 2) have been proposed. However, photosensitive resin compositions or polymers disclosed in these documents have a problem that the transparency is insufficient due to coloring of polyamide acid or the phenolic hydroxyl group.
As materials containing a siloxane compound excellent in transparency, a photosensitive siloxane composition containing a polysiloxane, a quinone diazide compound, a solvent and a thermally crosslinkable compound (e.g., Patent Document 3), and a high refractive index material containing a siloxane compound having an aromatic hydrocarbon group (e.g., Patent Document 4) have been proposed, but in recent years, a material capable of forming a cured film with a higher refractive index is required.
As siloxane-based materials having a high refractive index, a siloxane-based resin composition obtained by a method of hydrolyzing and condensing an alkoxysilane in the presence of metal compound particles (e.g., Patent Document 5) has been disclosed. However, since such a resin composition has insufficient sensitivity at the time of exposure and produces a minute residue of portion remaining undissolved in development, the resolution is insufficient.